The Effects of Obesity and Exercise on Myogenic Regulatory Factors

Abstract

This study tested the hypothesis that myogenic transcription factors (MRFs) MyoD and myogenin, would be lower in skeletal muscles of Obese Zucker rats (OZR) than age-matched lean rats (LZR), and that they would be restored with aerobic exercise. The extensor digitorum longus (EDL), soleus and medial gastrocnemius muscles (MG) were studied as representative of muscles predominantly containing fast, slow, and a mixture of both fast and slow myosin heavy chains (MHC) respectively. Myogenin protein content was 60% higher in control EDL muscles of OZR, but decreased with exercise. In contrast, MyoD content in EDL muscles was unchanged by exercise. Myogenin was 20% lower in soleus muscles of OZR than LZR and increased 85% following exercise training. Myogenin protein content was a 15% lower in MG muscles of OZR vs. LZR, but was restored with exercise. MyoD protein content in the MG was similar in OZR and LZR (p=0.10), and was unchanged with exercise. mRNA expression of MHC I and MHC IIa was 60 and 40%, lower respectively in MG of OZR than LZR. MHC IIb mRNA content was similar in MG from OZR and LZR. Exercise had no effect on MHC IIA or MHC IIB mRNA in the MG of OZR, but it restored MHC I expression to that found in LZR. These data indicate that MRFs are altered in a myosin specific manner and this accompanies reductions in MHC I and IIA mRNA in muscles of OZR. Myogenin was responsive to exercise in OZR. Supported by NIH AG021530.